The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Subframe mounts are used extensively in unibody vehicles to isolate vibrations created by road inputs from being transmitted from the engine to the subframe and the body, and vice versa. The operator of the vehicle perceives that vibration isolation relates to ride quality and that improved vehicle dynamics translates into improved handling performance.
Typically, there are as many as four locations on the sub-frame where an isolation mount is utilized. The sub-frame is compressed between the upper portion and the lower portion of the vibration mount and the vehicle body rests on top of the upper mount. A bolt extends through an aperture in the sub-frame and the isolation mount. The lower mount and the upper mount are connected by a weld nut on the body to complete the attachment, of the body to the sub-frame. The mount isolates road inputs and engine or transmission induced vibration that is transmitted along the sub-frame to the body. The mount also improves vehicle dynamics by controlling or attenuating relative movement between the vehicle body and sub-frame in the vertical mode or plane, that is up and down, relative movement, and also to control lateral mode or plane, that is side to side movement, and fore and aft mode or plane, that is front to back relative movement.
A typical design of a sub-frame isolation mount employs a relatively hard or high durometer rubber (typically 40 to 80 Shore A) as an isolating material. High durometer rubber for cradle or sub-frame mounts is an excellent material for improved handling in the lateral plane, especially when it is combined with rate plates to stiffen the response in the lateral plane and to a limited degree the fore and aft plane. However, since the solid elastomeric material is generally very stiff, it does not attenuate vertical forces from the subframe to the body very effectively. As a result, the isolation mount has a high lateral stiffness rate response which is desirable but it has a fore aft stiffness rate response which is marginally acceptable and a vertical stiffness rate response which is low. Therefore, good ride and handling of a vehicle are compromised because of the stiffness properties of the solid elastomeric material.
Thus, there is a need for a vibration isolation mount that provides for ride quality that is satisfactory to the operator without sacrificing the handling characteristics of the vehicle in the lateral plane, fore and aft plane and vertical plane. Additionally, there is a need for a mount that is lighter in weight, improves durability and reduces both initial and high mileage noise, vibration, and harshness between a sub-frame and a body.